[pmlnr]

http://dspam.nuclearelephant.com/

It's a bit picky and horribly documented, but extremely fast and low on resources.

[spotman]

Except database size. Will grow to gigs and gigs and gigs and gigs. Dspam can be very difficult to manage with a 400gb token database when you have a large system. ( last version I used was 3.9 maybe they have improved this?)